function runajax(){
    return new Promise((resolve,reject)=>{
        setTimeout(function(){
            console.log("hello world");
            resolve('西红柿');
        },2000);
    });
}
runajax();

var p=runajax();
p.then(function(ret){
    console.log("做饭......",ret);
})
console.log("函数外......");